Laser multipass welding techniques for thick section steels have been developed using a new type of UV combined narrow groove. The shape and sizes at the bottom of groove are determined by analyzing the plasma behavio...Laser multipass welding techniques for thick section steels have been developed using a new type of UV combined narrow groove. The shape and sizes at the bottom of groove are determined by analyzing the plasma behavior using high speed photographic equipment. A stable autogenous CO2 laser welding process and greater penetration are generated at the root pass because of strong reduction of the plasma volume. According to the waveforms of welding current and arc voltage, and the interaction between the arc and the laser induced plasma, a suitable groove angle is obtained. Laser-double MIG hybrid welding process is studied and the optimum distances between the laser and two arcs are determined. By using autogenous CO2 laser welding, CO2 laser-MIG hybrid welding and laser-double MIG hybrid welding, 28 mm thick steel plates are welded with four passes. The welds produced are assessed by X-ray. No crack is found and there is only a small amount of pores. The experimental results show that the multipuss welding procedures proposed can realize the joining of thick section steels with high efficiency and good quality.展开更多
Theoretical analysis model has been established for CO 2 laser to describe the process of dynamic emission in the electrooptically Q switched laser .The electron excitation and the energy transfer of vibration level a...Theoretical analysis model has been established for CO 2 laser to describe the process of dynamic emission in the electrooptically Q switched laser .The electron excitation and the energy transfer of vibration level and the rotational relaxation of rotational levels are described. The comparison between this model and a set of coupled rat equations model are discussed.展开更多
Objective: To study the effect of RFTVR and CO2 laser on the improvement of symptoms, QOL and vas of patients with early laryngeal cancer. Methods: In this study, 120 patients with laryngeal cancer diagnosed and treat...Objective: To study the effect of RFTVR and CO2 laser on the improvement of symptoms, QOL and vas of patients with early laryngeal cancer. Methods: In this study, 120 patients with laryngeal cancer diagnosed and treated from January 2015 to December 2016 were taken as research objects. All patients were randomly divided into observation group and control group, 60 patients in each group. Patients in observation group were treated with RFTVR, and patients in control group were treated with new-type fiber-optic CO2 laser. The patients in the two groups were treated with cisplatin injection. The differences of perioperative indexes, swallowing function, pronunciation function, survival period, QOL score and VAS score between the two groups were compared. Results: There was no significant difference in the amount of intraoperative bleeding, operation time and hospitalization time between the two groups (P > 0.05);the correct swallowing of the observation group was significantly higher than that of the control group. After treatment, jitter, shimmer and HNR of the two groups were significantly improved, and jitter and shimmer of the observation group were significantly lower than that of the control group, and HNR was significantly higher than that of the control group (P < 0.05) The QOL score and VAS score of the two groups were significantly improved, and the QOL score of the observation group was significantly higher than that of the control group and the VAS score was significantly lower than that of the control group (P < 0.05);the total survival period and tumor free survival period of the observation group were significantly higher than that of the control group. Conclusion: Compared with CO2 laser treatment, the swallowing function and voice function of patients treated by low temperature plasma radiofrequency ablation were significantly improved, and the life quality of patients was significantly improved by prolonging the survival period of patients..展开更多
Objective To investigate the clinical effect of botulinum toxin type A injection combined with low-energy CO2 fractional laser periocular rejuvenation treatment.Methods The clinical effect of botulinum type A injectio...Objective To investigate the clinical effect of botulinum toxin type A injection combined with low-energy CO2 fractional laser periocular rejuvenation treatment.Methods The clinical effect of botulinum type A injection alone and botulinum type A injection combined with low-energy CO2 fractional laser was compared in 96 patients who needed to receive periocular rejuvenation treatment from April 2018 to April 2019.Results After the combined low-energy CO2 fractional laser treatment was given on the basis of botulinum toxin type A injection,the follow-up global aesthetic improvement scale(GAIS)scores of the observation group were 86.78±4.67,80.31±3.66,76.94±4.03 and 40.59±4.78.The global aesthetic improvement of the dynamic and static wrinkles was obvious.The total effective rate was 93.7%.The total satisfaction rate of the patients was 95.8%,which was higher than that of the control group(P<0.05).The clinical efficacy was significant.Conclusion The application of the combined periocular rejuvenation treatment can improve the dynamic and static wrinkles simultaneously with remarkable rejuvenation effect,increase the effective rate of treatment and enhance the patients'satisfaction.展开更多
Objective: to analyze the clinical effect of carbon dioxide dot matrix laser cosmetic treatment in the treatment of skin diseases. Methods: 90 patients with skin diseases treated in our hospital were randomly divided ...Objective: to analyze the clinical effect of carbon dioxide dot matrix laser cosmetic treatment in the treatment of skin diseases. Methods: 90 patients with skin diseases treated in our hospital were randomly divided into control group (n = 45) and observation group (n = 45). The patients in the control group were treated with conventional topical drugs, and the patients in the observation group were treated with carbon dioxide dot matrix phototherapy on the basis of the control group. The treatment effects and treatment satisfaction of the two groups were compared. Results: the effective rate of the observation group (98.73%) was significantly higher than that of the control group (84.81%) (P < 0.05);The treatment satisfaction of patients in the observation group (%) was significantly higher than that in the control group (%). Conclusion: in the clinical treatment of skin diseases, the combined application of carbon dioxide dot matrix laser beauty treatment can obtain better clinical effect and has the value of clinical popularization and application.展开更多
Objective To observe the effect of uitrapulse CO2 laser combined with Erbium fractional laser on treatment facial scars. Methods Total 70 cases with facial scars were treated with ultrapulse CO2 laser combined with Er...Objective To observe the effect of uitrapulse CO2 laser combined with Erbium fractional laser on treatment facial scars. Methods Total 70 cases with facial scars were treated with ultrapulse CO2 laser combined with Erbium fractional laser for 3 times with 2 ～ 3 months interval. Firstly,scar resurfacing was performed展开更多
A new fully automatic ^40Ar/^39Ar laboratory with a Thermo Scientific ARGUS VI mass spectrometer has been established in China University of Geosciences （Wuhan）. We designed and developed a mini efficient preparatio...A new fully automatic ^40Ar/^39Ar laboratory with a Thermo Scientific ARGUS VI mass spectrometer has been established in China University of Geosciences （Wuhan）. We designed and developed a mini efficient preparation system （80 mL）, a CO2 laser for heating samples, a crusher for extracting fluid inclusions within K-poor minerals and an air reservoir （31 L） and pipette （0.1 mL） system. The ARGUS VI mass spectrometer is operated by the Qtegra Noble Gas software, which can control the peripheral accessories, such as pneumatic valves, CO2 laser and crusher through a PeriCon （peripheral controller）. The experimental procedures of atmospheric argon ana- lyses, ^40Ar/^39Ar dating by laser stepwise heating and by progressive crushing in vacuo, can be fully automatically performed. The weighted mean of atmospheric ^40Ar/^36Ar ratios is 302.22＋0.03 （1σ, MSWD=0.74, n=200）, indicating that air reservoir and pipette system and the whole instrument sys- tem are very stable. This laboratory is a successful pioneer example in China to establish a new no- ble gas laboratory with self-made peripheral accessories expect for the mass spectrometer.展开更多
A laser lap welding process for zinc-coated steel has a well-known unsolved problem-porosity formation. The boiling temperature of coated zinc is lower than the melting temperature of the base metal, which is steel. I...A laser lap welding process for zinc-coated steel has a well-known unsolved problem-porosity formation. The boiling temperature of coated zinc is lower than the melting temperature of the base metal, which is steel. In the autogenous laser welding, the zinc vapor generates from the lapped surfaces expels the molten pool and the expulsion causes numerous weld defects, such as spatters and blow holes on the weld surface and porosity inside the welds. The laser-arc hybrid welding was suggested as an alternative method for the laser lap welding because the arc can preheat or post-beat the weldment according to the arrangement of the laser beam and the arc. CO2 laser-micro plasma hybrid welding was applied to the lap welding of zinc-coated steel with zero-gap. The relationships among the weld quality and process parameters of the laser-arc arrangement, and the laser-arc interspacing distance and arc current were investigated using a full-factorial experimental design. The effect of laser-arc arrangement is dominant because the leading plasma arc partially melts the upper steel sheets and vaporizes or oxidizes the coated zinc on the lapped surfaces. Compared with the result from the laser-TIG hybrid welding, the heat input from arc can be reduced by 40%.展开更多
A non-evaporative technique is used to mitigate damage sites with lateral sizes in a range from 50 μm to 400 μm and depths smaller than 100 μm.The influence of the pulse frequency of a CO 2 laser on the mitigation ...A non-evaporative technique is used to mitigate damage sites with lateral sizes in a range from 50 μm to 400 μm and depths smaller than 100 μm.The influence of the pulse frequency of a CO 2 laser on the mitigation effect is studied.It is found that a more symmetrical and smooth mitigation crater can be obtained by increasing the laser pulse frequency form 0.1 to 20 kHz.Furthermore,the sizes of laser-affected and distorted zones decrease with the increase of the laser pulse frequency,leading to less degradation of the wave-front quality of the conditioned sample.The energy density of the CO 2 laser beam is introduced for selecting the mitigation parameters.The damage sites can be successfully mitigated by increasing the energy density in a ramped way.Finally,the laser-induced damage threshold（LIDT） of the mitigated site is tested using 355 nm laser beam with a small spot（0.23 mm 2） and a large spot（3.14 mm 2）,separately.It is shown that the non-evaporative mitigation technique is a successful method to stop damage re-initiation since the average LIDTs of mitigated sites tested with small or large laser spots are higher than that of pristine material.展开更多
The CO2 laser welding of BT20 titanium alloy and Ti-23Al-17Nb titanium aluminide was conducted to investigate into the porosity in titanium alloy weld. The results show that there are two sorts of porosities observed ...The CO2 laser welding of BT20 titanium alloy and Ti-23Al-17Nb titanium aluminide was conducted to investigate into the porosity in titanium alloy weld. The results show that there are two sorts of porosities observed in welds of titanium alloy laser welding based on the microscopic characteristics of the porosities. One is the metallurgical porosity with round and smooth inner wall, which results from the surface contamination. The other is the processing porosity with irregular and rough inner wall that displays the trace of the pool flowing, which results from the ruffle on the keyhole wall gathering together locally and closing down the gas in the keyhole into bubbles because of the keyhole fluctuating. The CO2 laser welding could break down easily the surface oxide film and produce little metallurgical porosity, but produces easily processing porosity when partial penetration or unstable-full penetration laser welding is conducted, which always occurs in the center of weld.展开更多
In this paper, a high-speed camera and an optical emission monitor were used to study the behavior of vapor/ plasma during CO2 laser welding of SUS304 stainless steel. Results of optical emission from vapor/plasma sho...In this paper, a high-speed camera and an optical emission monitor were used to study the behavior of vapor/ plasma during CO2 laser welding of SUS304 stainless steel. Results of optical emission from vapor/plasma show that two characteristic frequency bands exist, 100 -500 Hz and 1 500 -3 500 Hz. At the same time, the changing images of vapor/ plasma and bottom pool also confirm that there are two different fluctuation frequency bands. One of the frequency bands represents the characteristic of vapor/plasma within the keyhole, and it is within 167 -500 Hz. Another frequency band is within 1 500 - 3 500 Hz, and it obviously derives from the shielding gas. Some factors may cause these frequency differences between the keyhole plasma and the shielding gas plasma. One of them is that the vapor/plasma pressure within the keyhole will increase slowly.展开更多
Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructura...Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructural features of the welded joint were investigated. The increase of welding speed reduced the width of the weld bead and the porosities in the weld bead resulting from the different flow mode of melted metal in weld pool. The decrease of welding power or use of shield gas of helium also contributed to the reduction of porosity in the weld bead due to the alleviation of induced plasma formation, thus stabilizing the keyhole. The porosity formation intimately correlated with the evaporation of alloy element Mn in the base metal. The laser welded metal had same martensite microstructure as that of water-quenched base metal. The welding parameters which increased cooling rate all led to fine microstructures of the weld bead.展开更多
A theory of the far spatial coherent-suppressed single-peak field distribution of a rectangular wave-guide CO2 laser is presented. The theoretical analysis shows that a rectangular wave-guide laser can have an output ...A theory of the far spatial coherent-suppressed single-peak field distribution of a rectangular wave-guide CO2 laser is presented. The theoretical analysis shows that a rectangular wave-guide laser can have an output intensity distribution in far field similar to that produced from a wave-guide array laser, which is in agreement with the experimental result. A single-peak mode output is obtained within 5 metres. The experimental far-field spread angle in the bigger-Fresnel number direction is 0.63 mrad, compared to the calculated one, 0.6 mrad, and when the length of the laser resonator is changed, a double-peak or multi-peak in far-field distribution of the laser is obtained.展开更多
The technology of CO2 laser welding and joint properties of titanium alloy were investigated. The problem of molten pool protection was resolved by designing a shielding trailer and a special clamp. Joints with silver...The technology of CO2 laser welding and joint properties of titanium alloy were investigated. The problem of molten pool protection was resolved by designing a shielding trailer and a special clamp. Joints with silvery appearance were obtained, which have no pore and crack. In addition, the welding speed could reach 3 m/min for the plate of 1.5 mm thickness being penetrated. The reason of the porosity formation in partial penetration joints is that the keyholes can be easily cut apart in the radial direction, which makes the gas enclosed in the molten pool. The surface oxide of specimens can not affect the porosity formation in welds directly.展开更多
In order to improve the weldability of duplex stainless steels,obtaining more secondary austenite in the weld metal is an effective way.Therefore,optimizing the secondary austenite by changing its morphology,volume fr...In order to improve the weldability of duplex stainless steels,obtaining more secondary austenite in the weld metal is an effective way.Therefore,optimizing the secondary austenite by changing its morphology,volume fraction and stability may be expected to enhance the ductility of the weld.The secondary austenite morphologies in the fusion zone of the laser continuously heat treated welds of 2205 duplex stainless steel were investigated.The secondary austenite morphologies were found to be influenced by different laser power level.The secondary austenite with penniform,freely grown and dendritic shape appeared in the course of 4,6 and 8 kW continuous heat treatment,respectively.It was found that there were three kinds of morphologies of secondary austenite in the fusion zone treated by different power,i.e.,widmannst¨atten austenite,grain boundary austenite and intragranular austenite.The results demonstrated that the mechanism of the secondary austenite formation was a displacement mechanism during the initial austenite lath formation and a diffusion mechanism during cooling.The nitrides provided the nitrogen for the transformation and at the same time acted as nucleation sites for the secondary austenite.展开更多
To understand the surface morphology evolution of fused silica induced by 10.6μm CO2 laser irradiation at different parameters, this paper reports that optical microscopy, profilometry, and hydrophilicity tests are u...To understand the surface morphology evolution of fused silica induced by 10.6μm CO2 laser irradiation at different parameters, this paper reports that optical microscopy, profilometry, and hydrophilicity tests are utilized to characterize the surface structure and roughness of the laser irradiated area. The results show that three typical surface morphologies and two typical hydrophilicity test images are observed at different laser powers and pulse durations. The correlations between surface temperature and surface morphology as well as hydrophilicity behaviours are presented. The different hydrophilicity behaviours are related to surface structures of the laser-induced crater and thermal diffusion area. The thermal diffusion length monotonously increases with increasing laser power and pulse duration. The crater width is almost determined by the laser beam size. The crater depth is more sensitive to the laser power and pulse duration than the crater width.展开更多
To study hollow waveguides for CO 2 laser transmission,a liquid-phase depositi on technique is applied to form a silver film inside silica capillary based on t he method of silver mirror reaction.Using this fabricati...To study hollow waveguides for CO 2 laser transmission,a liquid-phase depositi on technique is applied to form a silver film inside silica capillary based on t he method of silver mirror reaction.Using this fabrication method,the optimum co mbination of different parameters is gained and hollow waveguides have been made successfully with a bore size of 1mm and a guide with length of as long as 2m o n self-producing apparatus.To meet quality silver film,a relative high temperat ure,low flowing speed and long time are adopted on the basis of low reactant con centration.The maximum transmission efficiency of hollow-core fiber without die lectric coating can be up to 85 percent and loss can be low to 0.5dB/m,maximum o utput power is 53W for stable 20mintues.展开更多
A CW CO2 laser collective Thomson scattering diagnostics was developed to measure plasma density fluctuations on the HT-7 tokamak. The design and construction of CO2 laser scattering apparatus is described. The laser ...A CW CO2 laser collective Thomson scattering diagnostics was developed to measure plasma density fluctuations on the HT-7 tokamak. The design and construction of CO2 laser scattering apparatus is described. The laser source is a continuous-wave CO2 laser with a cavity length of 1.9 m and a power output of about 10 W at 10.6 μm. The k-resolution of the system is △k ≈ 3.2 cm-1. The preliminary data from the diagnostic is presented.展开更多
文摘Laser multipass welding techniques for thick section steels have been developed using a new type of UV combined narrow groove. The shape and sizes at the bottom of groove are determined by analyzing the plasma behavior using high speed photographic equipment. A stable autogenous CO2 laser welding process and greater penetration are generated at the root pass because of strong reduction of the plasma volume. According to the waveforms of welding current and arc voltage, and the interaction between the arc and the laser induced plasma, a suitable groove angle is obtained. Laser-double MIG hybrid welding process is studied and the optimum distances between the laser and two arcs are determined. By using autogenous CO2 laser welding, CO2 laser-MIG hybrid welding and laser-double MIG hybrid welding, 28 mm thick steel plates are welded with four passes. The welds produced are assessed by X-ray. No crack is found and there is only a small amount of pores. The experimental results show that the multipuss welding procedures proposed can realize the joining of thick section steels with high efficiency and good quality.
文摘Theoretical analysis model has been established for CO 2 laser to describe the process of dynamic emission in the electrooptically Q switched laser .The electron excitation and the energy transfer of vibration level and the rotational relaxation of rotational levels are described. The comparison between this model and a set of coupled rat equations model are discussed.
基金State key laboratory of medical immunology open project (NKMI2019K07)
文摘Objective: To study the effect of RFTVR and CO2 laser on the improvement of symptoms, QOL and vas of patients with early laryngeal cancer. Methods: In this study, 120 patients with laryngeal cancer diagnosed and treated from January 2015 to December 2016 were taken as research objects. All patients were randomly divided into observation group and control group, 60 patients in each group. Patients in observation group were treated with RFTVR, and patients in control group were treated with new-type fiber-optic CO2 laser. The patients in the two groups were treated with cisplatin injection. The differences of perioperative indexes, swallowing function, pronunciation function, survival period, QOL score and VAS score between the two groups were compared. Results: There was no significant difference in the amount of intraoperative bleeding, operation time and hospitalization time between the two groups (P > 0.05);the correct swallowing of the observation group was significantly higher than that of the control group. After treatment, jitter, shimmer and HNR of the two groups were significantly improved, and jitter and shimmer of the observation group were significantly lower than that of the control group, and HNR was significantly higher than that of the control group (P < 0.05) The QOL score and VAS score of the two groups were significantly improved, and the QOL score of the observation group was significantly higher than that of the control group and the VAS score was significantly lower than that of the control group (P < 0.05);the total survival period and tumor free survival period of the observation group were significantly higher than that of the control group. Conclusion: Compared with CO2 laser treatment, the swallowing function and voice function of patients treated by low temperature plasma radiofrequency ablation were significantly improved, and the life quality of patients was significantly improved by prolonging the survival period of patients..
文摘Objective To investigate the clinical effect of botulinum toxin type A injection combined with low-energy CO2 fractional laser periocular rejuvenation treatment.Methods The clinical effect of botulinum type A injection alone and botulinum type A injection combined with low-energy CO2 fractional laser was compared in 96 patients who needed to receive periocular rejuvenation treatment from April 2018 to April 2019.Results After the combined low-energy CO2 fractional laser treatment was given on the basis of botulinum toxin type A injection,the follow-up global aesthetic improvement scale(GAIS)scores of the observation group were 86.78±4.67,80.31±3.66,76.94±4.03 and 40.59±4.78.The global aesthetic improvement of the dynamic and static wrinkles was obvious.The total effective rate was 93.7%.The total satisfaction rate of the patients was 95.8%,which was higher than that of the control group(P<0.05).The clinical efficacy was significant.Conclusion The application of the combined periocular rejuvenation treatment can improve the dynamic and static wrinkles simultaneously with remarkable rejuvenation effect,increase the effective rate of treatment and enhance the patients'satisfaction.
文摘Objective: to analyze the clinical effect of carbon dioxide dot matrix laser cosmetic treatment in the treatment of skin diseases. Methods: 90 patients with skin diseases treated in our hospital were randomly divided into control group (n = 45) and observation group (n = 45). The patients in the control group were treated with conventional topical drugs, and the patients in the observation group were treated with carbon dioxide dot matrix phototherapy on the basis of the control group. The treatment effects and treatment satisfaction of the two groups were compared. Results: the effective rate of the observation group (98.73%) was significantly higher than that of the control group (84.81%) (P < 0.05);The treatment satisfaction of patients in the observation group (%) was significantly higher than that in the control group (%). Conclusion: in the clinical treatment of skin diseases, the combined application of carbon dioxide dot matrix laser beauty treatment can obtain better clinical effect and has the value of clinical popularization and application.
文摘Objective To observe the effect of uitrapulse CO2 laser combined with Erbium fractional laser on treatment facial scars. Methods Total 70 cases with facial scars were treated with ultrapulse CO2 laser combined with Erbium fractional laser for 3 times with 2 ～ 3 months interval. Firstly,scar resurfacing was performed
基金financially supported by the National Natural Science Foundation of China (Nos. 41503053, 41630315, 41688103, and 91128203)
文摘A new fully automatic ^40Ar/^39Ar laboratory with a Thermo Scientific ARGUS VI mass spectrometer has been established in China University of Geosciences （Wuhan）. We designed and developed a mini efficient preparation system （80 mL）, a CO2 laser for heating samples, a crusher for extracting fluid inclusions within K-poor minerals and an air reservoir （31 L） and pipette （0.1 mL） system. The ARGUS VI mass spectrometer is operated by the Qtegra Noble Gas software, which can control the peripheral accessories, such as pneumatic valves, CO2 laser and crusher through a PeriCon （peripheral controller）. The experimental procedures of atmospheric argon ana- lyses, ^40Ar/^39Ar dating by laser stepwise heating and by progressive crushing in vacuo, can be fully automatically performed. The weighted mean of atmospheric ^40Ar/^36Ar ratios is 302.22＋0.03 （1σ, MSWD=0.74, n=200）, indicating that air reservoir and pipette system and the whole instrument sys- tem are very stable. This laboratory is a successful pioneer example in China to establish a new no- ble gas laboratory with self-made peripheral accessories expect for the mass spectrometer.
文摘A laser lap welding process for zinc-coated steel has a well-known unsolved problem-porosity formation. The boiling temperature of coated zinc is lower than the melting temperature of the base metal, which is steel. In the autogenous laser welding, the zinc vapor generates from the lapped surfaces expels the molten pool and the expulsion causes numerous weld defects, such as spatters and blow holes on the weld surface and porosity inside the welds. The laser-arc hybrid welding was suggested as an alternative method for the laser lap welding because the arc can preheat or post-beat the weldment according to the arrangement of the laser beam and the arc. CO2 laser-micro plasma hybrid welding was applied to the lap welding of zinc-coated steel with zero-gap. The relationships among the weld quality and process parameters of the laser-arc arrangement, and the laser-arc interspacing distance and arc current were investigated using a full-factorial experimental design. The effect of laser-arc arrangement is dominant because the leading plasma arc partially melts the upper steel sheets and vaporizes or oxidizes the coated zinc on the lapped surfaces. Compared with the result from the laser-TIG hybrid welding, the heat input from arc can be reduced by 40%.
基金Project supported by the National High Technology Research and Development Program of China(Grant No.2008AA8040508)Foundation for Young Scholars of University of Electronic Science and Technology of China(Grant No.L08010401JX0806)+2 种基金the Joint Fund of the National Natural Science Foundation of China and the China Academy of Engineering Physics(Grant No.11076008)the Fundamental Research Funds for the Central Universities of China(Grant No.ZYGX2011J043)the Sichuan Provincial Young Scientists Foundation,China(Grant No.2010JQ0006)
文摘A non-evaporative technique is used to mitigate damage sites with lateral sizes in a range from 50 μm to 400 μm and depths smaller than 100 μm.The influence of the pulse frequency of a CO 2 laser on the mitigation effect is studied.It is found that a more symmetrical and smooth mitigation crater can be obtained by increasing the laser pulse frequency form 0.1 to 20 kHz.Furthermore,the sizes of laser-affected and distorted zones decrease with the increase of the laser pulse frequency,leading to less degradation of the wave-front quality of the conditioned sample.The energy density of the CO 2 laser beam is introduced for selecting the mitigation parameters.The damage sites can be successfully mitigated by increasing the energy density in a ramped way.Finally,the laser-induced damage threshold（LIDT） of the mitigated site is tested using 355 nm laser beam with a small spot（0.23 mm 2） and a large spot（3.14 mm 2）,separately.It is shown that the non-evaporative mitigation technique is a successful method to stop damage re-initiation since the average LIDTs of mitigated sites tested with small or large laser spots are higher than that of pristine material.
文摘The CO2 laser welding of BT20 titanium alloy and Ti-23Al-17Nb titanium aluminide was conducted to investigate into the porosity in titanium alloy weld. The results show that there are two sorts of porosities observed in welds of titanium alloy laser welding based on the microscopic characteristics of the porosities. One is the metallurgical porosity with round and smooth inner wall, which results from the surface contamination. The other is the processing porosity with irregular and rough inner wall that displays the trace of the pool flowing, which results from the ruffle on the keyhole wall gathering together locally and closing down the gas in the keyhole into bubbles because of the keyhole fluctuating. The CO2 laser welding could break down easily the surface oxide film and produce little metallurgical porosity, but produces easily processing porosity when partial penetration or unstable-full penetration laser welding is conducted, which always occurs in the center of weld.
文摘In this paper, a high-speed camera and an optical emission monitor were used to study the behavior of vapor/ plasma during CO2 laser welding of SUS304 stainless steel. Results of optical emission from vapor/plasma show that two characteristic frequency bands exist, 100 -500 Hz and 1 500 -3 500 Hz. At the same time, the changing images of vapor/ plasma and bottom pool also confirm that there are two different fluctuation frequency bands. One of the frequency bands represents the characteristic of vapor/plasma within the keyhole, and it is within 167 -500 Hz. Another frequency band is within 1 500 - 3 500 Hz, and it obviously derives from the shielding gas. Some factors may cause these frequency differences between the keyhole plasma and the shielding gas plasma. One of them is that the vapor/plasma pressure within the keyhole will increase slowly.
文摘Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructural features of the welded joint were investigated. The increase of welding speed reduced the width of the weld bead and the porosities in the weld bead resulting from the different flow mode of melted metal in weld pool. The decrease of welding power or use of shield gas of helium also contributed to the reduction of porosity in the weld bead due to the alleviation of induced plasma formation, thus stabilizing the keyhole. The porosity formation intimately correlated with the evaporation of alloy element Mn in the base metal. The laser welded metal had same martensite microstructure as that of water-quenched base metal. The welding parameters which increased cooling rate all led to fine microstructures of the weld bead.
文摘A theory of the far spatial coherent-suppressed single-peak field distribution of a rectangular wave-guide CO2 laser is presented. The theoretical analysis shows that a rectangular wave-guide laser can have an output intensity distribution in far field similar to that produced from a wave-guide array laser, which is in agreement with the experimental result. A single-peak mode output is obtained within 5 metres. The experimental far-field spread angle in the bigger-Fresnel number direction is 0.63 mrad, compared to the calculated one, 0.6 mrad, and when the length of the laser resonator is changed, a double-peak or multi-peak in far-field distribution of the laser is obtained.
文摘The technology of CO2 laser welding and joint properties of titanium alloy were investigated. The problem of molten pool protection was resolved by designing a shielding trailer and a special clamp. Joints with silvery appearance were obtained, which have no pore and crack. In addition, the welding speed could reach 3 m/min for the plate of 1.5 mm thickness being penetrated. The reason of the porosity formation in partial penetration joints is that the keyholes can be easily cut apart in the radial direction, which makes the gas enclosed in the molten pool. The surface oxide of specimens can not affect the porosity formation in welds directly.
基金support from the National Basic Research Program of China(973 Program,No. 2010CB630800)the Shanghai Municipal Science and Technology Commission Foundation of China (Grant No. 0852nm02500)
文摘In order to improve the weldability of duplex stainless steels,obtaining more secondary austenite in the weld metal is an effective way.Therefore,optimizing the secondary austenite by changing its morphology,volume fraction and stability may be expected to enhance the ductility of the weld.The secondary austenite morphologies in the fusion zone of the laser continuously heat treated welds of 2205 duplex stainless steel were investigated.The secondary austenite morphologies were found to be influenced by different laser power level.The secondary austenite with penniform,freely grown and dendritic shape appeared in the course of 4,6 and 8 kW continuous heat treatment,respectively.It was found that there were three kinds of morphologies of secondary austenite in the fusion zone treated by different power,i.e.,widmannst¨atten austenite,grain boundary austenite and intragranular austenite.The results demonstrated that the mechanism of the secondary austenite formation was a displacement mechanism during the initial austenite lath formation and a diffusion mechanism during cooling.The nitrides provided the nitrogen for the transformation and at the same time acted as nucleation sites for the secondary austenite.
基金supported by the National High Technology Research and Development Program of China (Grant No. 2008AA8040508)the Foundation for Young Scholars of University of Electronic Science and Technology of China (Grant No. L08010401JX0806)
文摘To understand the surface morphology evolution of fused silica induced by 10.6μm CO2 laser irradiation at different parameters, this paper reports that optical microscopy, profilometry, and hydrophilicity tests are utilized to characterize the surface structure and roughness of the laser irradiated area. The results show that three typical surface morphologies and two typical hydrophilicity test images are observed at different laser powers and pulse durations. The correlations between surface temperature and surface morphology as well as hydrophilicity behaviours are presented. The different hydrophilicity behaviours are related to surface structures of the laser-induced crater and thermal diffusion area. The thermal diffusion length monotonously increases with increasing laser power and pulse duration. The crater width is almost determined by the laser beam size. The crater depth is more sensitive to the laser power and pulse duration than the crater width.
基金Funded by the Natural Science Foundation of Hubei Province (No.2002AB078)and the Foundation of Wuhan University Academy of Sciences(No.XJJ2002083)
文摘To study hollow waveguides for CO 2 laser transmission,a liquid-phase depositi on technique is applied to form a silver film inside silica capillary based on t he method of silver mirror reaction.Using this fabrication method,the optimum co mbination of different parameters is gained and hollow waveguides have been made successfully with a bore size of 1mm and a guide with length of as long as 2m o n self-producing apparatus.To meet quality silver film,a relative high temperat ure,low flowing speed and long time are adopted on the basis of low reactant con centration.The maximum transmission efficiency of hollow-core fiber without die lectric coating can be up to 85 percent and loss can be low to 0.5dB/m,maximum o utput power is 53W for stable 20mintues.
文摘A CW CO2 laser collective Thomson scattering diagnostics was developed to measure plasma density fluctuations on the HT-7 tokamak. The design and construction of CO2 laser scattering apparatus is described. The laser source is a continuous-wave CO2 laser with a cavity length of 1.9 m and a power output of about 10 W at 10.6 μm. The k-resolution of the system is △k ≈ 3.2 cm-1. The preliminary data from the diagnostic is presented.
